1. Field of the Invention
The present invention generally relates to an endoscope, and more particularly, to a heat radiation structure at the front end portion of the endoscope.
2. Description of the Related Art
Due to the introduction of medical endoscopes, the early detection rate of a disease is enhanced. Furthermore, as an endoscopy operation is made feasible, it becomes possible to prevent a side effect caused by an open abdominal operation or the like. Accordingly, the use of endoscopes has gradually increased in the medical field. In addition, as the size of endoscopes has been reduced and narrowed in order to lessen patients' pains, demands for an endoscope with a high resolution image sensor have also increased. Furthermore, it is obvious that a sufficient amount of light should be provided through an illumination device in order to satisfy the high resolution of an image sensor.
Two types of illumination for an endoscope are typically provided. The first type of illumination is to position a light source in an endoscope equipment body side, in other words, outside of a patient, and to arrange a light wave guide, such as an optical fiber, within an insertion tube to transmit light to the front end portion of the endoscope. In such a case, a lens may be mounted on the front end portion of the endoscope. The second type of illumination is configured such that a light source is directly mounted on the front end portion of the endoscope, in which case a power line connected to the light source should be provided in place of the light wave guide. That is, in the second type of illumination, the light source is inserted into the inside of the patient's body.
In the first type of illumination, it is not required to take heating by the light source into consideration because the light source is positioned outside of the patient's body. However, in the second type of illumination, because the light source is inserted into the patient's body, damage to a human anatomy by the heating of the light source or the like must be taken into consideration. Meanwhile, in the first type of illumination, the light should be transmitted through the light wave guide over a considerable length, and the light wave guide is curved many times inside of the patient's body. Accordingly, it is unavoidable that light is lost while the light is progressing in the light wave guide, and hence there is a limit in providing sufficient illumination for securing a high resolution image. The second type of illumination allows light produced from the light source to be used without loss because the light source is directly mounted on the front end portion of the endoscope. Accordingly, as the resolution of the image sensor of the endoscope is increased, the second type of illumination becomes more useful. However, as described above, with the second type of illumination, damage to the human anatomy caused by heating of the light source should be prevented. Therefore, the second type of illumination is preferably provided with a heat radiating and/or cooling structure in the front end portion of the endoscope.
U.S. Pat. No. 7,914,448 discloses a configuration in which a cooling chamber is formed on a base member where a circuit board is supported, and a heat exchanger is arranged in the cooling chamber. In the this configuration, cooling water circulates inside of the heat exchanger to cool the circuit board where the light source is arranged.
However, in the heat radiating structure of such a cooling water circulation type, it is feared that the cooling water may leak out. In addition, there is a limit in increasing the diameter of the cooling medium tube under the condition that the endoscope should remain narrow. Accordingly, there is a limit in increasing the circulation rate and volume of the cooling water, and consequently, it is unavoidable that the cooling performance is limited.
U.S. Patent Pub. No. 2010-317922 discloses a configuration in which cooling water is circulated to a heat exchanger through a fluid supply channel and a fluid discharge channel, and is controlled using a valve. A light source and an image sensor are arranged adjacent to the heat exchanger to be heat-radiated and cooled according to the circulation of the cooling water.
In the heat radiating structure with the above-mentioned structure, it is unavoidable that the front end portion is increased in size due to the valve arranged therein. In addition, since the fluid supply channel and the fluid discharge channel are separately configured, there are disadvantages in that it is unavoidable that the diameter of the endoscope is increased, and the flexibility of manipulation is deteriorated.
Japanese Patent Pub. No. 2007-007321 discloses a configuration in which an air conduit is arranged between a light source and an image sensor to cool the light source and the image sensor.
The heat radiating structure using the air conduit is limited in increasing the contact area between the cooling medium and a heating element, and if the air conduit is divided into a plurality of branches in order to increase the contact area, there is a problem in that the size of the front end portion of the endoscope is increased.
U.S. Patent Pub. No. 2011-0092772 discloses a configuration in which power is supplied to a light source and heat generated from the light source is transferred using an electric conductor.
However, if the diameter of the electric conductor is increased inside of the endoscope, the flexibility of manipulation is deteriorated. If the diameter of the electric conductor is reduced, the contact area with the light source is reduced, thereby unavoidably reducing the heat conductivity. Even if the heat conductivity is secured by increasing the diameter of the electric conductor while somewhat sacrificing the manipulation flexibility, this will cause the thickness of the front end portion of the endoscope to be increased.